Mysterious Disease Plaguing Bald Eagles

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Besides this information, little else is known. As Fischer says, "In the absence of reliable data, everyone's opinion is valid."

Needle in a Haystack Search

Part of the problem is the disease is likely caused by an outside agent—not by a virus or bacterium that could simply be extracted from the brains of diseased birds. And searching for a cause in the varied and vast habitat of the birds is not easy.

"We're suspicious it might be a chemical from an algae or plant," says Rocke. "It could also be a man-made pollutant or an exotic plant agent. But we really have nothing to confirm these ideas."

One common factor scientists have traced is the fact that all the diseased birds have been found around man-made reservoirs. Rocke explains this finding is not terribly revealing since many of the freshwater lakes in the Southeast are man-made.

Also puzzling is that people are known to get brain lesions similar to the ones that stem from the bird disease. But unlike the eagles and coots, people generally recover. Fischer says the human problems are thought to be related to substances like hexachlorophene that were once used in baby soap.

Clues Leading Nowhere

Tests of diseased bird tissue have shown no signs of hexachlorophene or other chemicals that have been shown to trigger lesions in human brains.

Another discovery that has led nowhere is the finding that mammals feeding on a group of toxic plants have come down with similar symptoms. But the plants are only found in Australia.

"We've done chemical analyses for all the chemicals that cause similar lesions in mammals and never found them in the birds," says Rocke.

As pathologists scour water systems for causes, Fischer worries the disease may already be taking hold in new areas.

"Truth be told, this disease could have been around for much longer and it just wasn't noticed," says Fischer. "It could very well be occurring on a more widespread basis than we realize."

And right now, there is little scientists can do to stop it.

Copyright 2001

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